1. Field of the Invention
The present invention relates in general to the field of automotive electrical systems. Specifically, the present invention is directed to a starting apparatus of an internal combustion engine including a starter/alternator assembly and a method for controlling transition of the starter/alternator assembly from a starting mode to a generation mode by monitoring a rotational speed of the starter/alternator assembly.
2. Description of the Prior Art
A recent trend in automotive electrical systems is the combining of the formerly separately functioning and operating starter and alternator/generator components. As automobiles become more electronics intensive, in terms of electronic accessories and sophistication of control systems, the need becomes greater for increased electrical supply. As a result, the alternator has become physically larger and more powerful as automotive electrical needs have increased.
In addition, the need for increasing operating efficiencies from internal combustion (I.C.) engines mandates a powerful and frequently operated starter motor to resume I.C. engine operation on short demand cycles. And, while these separate trends have been in place, a third element always present in automotive design is packaging efficiency in terms of under-hood space. As these trends have progressed, a commonly proposed strategy is to combine the starter and alternator/generator into a single under-hood starter/alternator assembly. During initial startup of the vehicle, the starter/alternator assembly functions as a starter. While functioning as a starter, the starter/alternator assembly provides a sufficient amount of torque to rotate the crankshaft of the engine before the cylinders are fired. After the engine is started, the starter/alternator assembly is used as a generator to provide electric power to the electrical system of the vehicle.
In this regard, the starter function of the starter/alternator assembly can be quite powerful vis-à-vis the I.C. engine being started inasmuch as the I.C. engine is required to achieve self-sustaining operation within xc2xd to 1 second of starter initiation and require significant demand of the battery. Furthermore, because of the increased demand of vehicle electrical systems, the capacity of the alternator is large and may generate substantial current during generation mode. The generator function of the starter/alternator assembly can be equally powerful vis-à-vis the capacity of the I.C. engine to generate sufficient torque especially during instances of high relative load and low relative engine speed.
In the above-described engine starting or cranking operation, it is desired to crank the engine with as large torque as possible to speedily start the engine by overcoming its large load resistance including static friction at the time of initial period of engine starting.
In the last period of engine starting after the engine is started to rotate, the engine starts to produce a driving torque and frictions at various friction surfaces in the engine changes from the static one to the dynamic one to reduce the load resistance. As a result, the rotational speed of the engine increases rapidly and large vibrations and noises are generated, thus degrading quietness and durability of the engine. Further, applying a large torque from the starter/alternator assembly to the engine to rapidly increase its rotational speed after the starting of engine rotation causes unnecessary consumption of electric power in a vehicle-mounted storage battery.
The present invention provides a novel arrangement of an apparatus and method for controlling a starter/alternator assembly of an internal combustion engine of a motor vehicle.
The present invention is directed to solving at least one of the potential problems associated with the trend towards combined starter and alternator functions and short demand cycle internal combustion (I.C.) engine operation of a motor vehicle. Specifically, the present invention provides a novel arrangement of an apparatus for starting the I.C. engine including a starter/alternator assembly, and a method for controlling the engine starting apparatus.
The apparatus for starting the I.C. engine in the motor vehicle, in accordance with the present invention, comprises a starter/alternator assembly operatively coupled to the engine and capable of being operated in a starter mode for starting the I.C. engine and in a generator mode for generating electric power when driven by the engine for supplying electrical power to an electrical load equipment. The starter/alternator assembly, in turn, includes a starter/alternator machine drivingly connected to the I.C. engine, an inverter provided for controlling an output of the starter/alternator machine to selectively choose either the starting mode or the generation mode for the starter/alternator machine, and an electronic controller provided for controlling the starter/alternator assembly. The starting apparatus further comprises a starter/alternator speed sensor for monitoring a rotational speed of the starter/alternator, which is electrically connected to the inverter of the starter/alternator. The starter/alternator speed is sensed directly from a rotation and/or position sensor mounted to the starter/alternator for monitoring a rotational speed of a rotor of the starter/alternator machine.
The method of the present invention controls transition of the starter/alternator assembly from the starter mode to a generator mode in response to the rotational speed of the starter/alternator directly sensed by the starter/alternator speed sensor.
In accordance with the first embodiment of the present invention, the electronic controller of the inverter produces an engine cranking indicative signal if the starter/alternator speed decreases. Then, if the starter/alternator speed increases after the engine cranking indicative signal was produced, the starter/alternator inverter produces an engine start indicative signal, and the controller instructs the starter/alternator inverter to disable the starter mode of the starter/alternator assembly in response to the engine start indicative signal. Finally, the controller instructs the starter/alternator inverter to enable the generator mode of the starter/alternator assembly.
In accordance with the second embodiment of the present invention, the inverter controller produces an engine cranking indicative signal when the starter/alternator speed reaches a first threshold value. Then, when the starter/alternator speed decreases to a second threshold value, the inverter controller produces an engine start indicative signal if the engine cranking indicative signal was already produced. Next, the inverter controller instructs the starter/alternator inverter to disable the starter mode of the starter/alternator assembly if the starter/alternator speed reaches a third threshold value after the engine start indicative signal was produced. Finally, the inverter controller instructs the starter/alternator inverter to enable the generator mode of the starter/alternator assembly.
The novel arrangement of an apparatus and method for controlling a starter/alternator assembly of an internal combustion engine of a motor vehicle in accordance with the present invention is effective to reduce engine vibration and noise, improve durability of the I.C. engine and the starter/alternator assembly, and quickly restore capacity of an electric storage battery.